1. Field of the Invention
The present invention relates to a brake friction pad for use in a disc brake mechanism or the like for braking an automobile, and, more particularly, to a brake friction pad having a wear warning piece for providing a warning of the wear limit of the lining of the brake friction pad.
2. Prior Art
FIGS. 1 and 2 show an example of a conventional brake friction pad.
Referring to FIGS. 1 and 2, reference numeral 1 designates a friction pad and 2 represents a backing plate of the friction pad 1. A pair of lugs 2A are so formed on the two sides of the backing plate 2 as to project laterally of the backing plate 2, the lugs 2A being adapted to be movably supported by a carrier (omitted from the illustration) of a disk brake. The backing plate 2 has circular punched holes 2B formed therein, the punched holes 2B acting to position a lining 5 to be secured to a side 2C of the backing plate 2.
Reference numeral 3 designates a circular recessed portion formed in the side 2C of the backing plate 2 at the lower left position of the backing plate 2 when viewed in the drawing, the recessed portion 3 being press-formed by using a punch (omitted from the illustration). Reference numeral 4 represents a projection to be riveted (shown after being riveted in the figure) formed on the other side 2D of the backing plate 2, the projection 4 being formed by using a die (omitted from the illustration) so positioned on the surface of the side 2D as to correspond to the position of the punch for forming the recessed portion 3. As a result, the projection 4 is formed by the die simultaneously with the forming of the recessed portion 3 by the punch.
Reference numeral 5 designates a lining secured to the side 2C of the backing plate 2, the lining 5 being made of a resin the base material which is a sintered metal or asbestos and which also fills the punched holes 2B and recessed portion 3. The lining 5 is pressed to a disc (omitted from the illustration) which rotates when the brake mechanism is operated so that it is moved into contact with the surface of the disc. As a result, a braking force is applied to the disc.
Reference numeral 6 designates a wear limit warning piece acting to notify a driver of the fact that the lining 5 has reached its wear limit. The wear limit warning piece 6 is manufactured by bending an elongated plate such as a steel plate having a spring effect by means of press forming or the like. A base portion 6A of the wear limit warning piece 6 is placed in contact with the side 2D of the backing plate 2 in such a manner that the projection 4 formed on the backing plate 2 is fitted in a hole 6B formed in the base portion 6A, and then riveted.
Assuming that the projection length of a front portion 6C of the wear limit warning piece 6 over the side 2C of the backing plate 2 in the thickness direction of the lining 5 is a, it is expressed by the following equation: EQU a=L.sub.1 -L.sub.2 -S (1)
where
L.sub.1 : the overall length of the wear limit warning piece 6 PA1 L.sub.2 : the length from the side 2D of the backing plate 2 to the top end of the wear limit warning piece 6 PA1 S: the thickness of the backing plate 2
As a result, when the above-described lining 5 has been worn down to its wear limit, the front portion 6C of the wear limit warning piece 6 is brought into contact with the surface of the disc rotating so that vibration causing a large amount of noise is generated. Thus, the fact that the lining 5 has reached its wear limit becomes obvious to a driver.
Another conventional technology will be described with reference to FIG. 3.
In general, there is a possibility of resonance being generated during operation of the braking mechanism due to a proximity or coincidence of the particular frequency of each of the braking mechanism parts, depending upon the dimensions of the parts such as the caliper, the friction pad and the disc. In order to prevent the above-described resonance or in order to change the thickness of the friction pad for other purposes, friction pad 1' has been employed which comprises a backing plate 2' having thickness S' which is smaller than the thickness S of the aforementioned conventional backing plate 2. If the friction pad 1' of the type just described above is assembled with the above-described wear limit warning piece 6 used as it is, the wear limit warning piece 6 projects in excess of a determined projection arranged to correspond to the wear limit thickness of the lining 5 by .DELTA.S (where .DELTA.S=S-S') which is the degree of the reduction in thickness when the backing plate 2' is designed.
In order to prevent this problem, a wear limit warning piece 6' having length L.sub.1 ' arranged to correspond to the thin backing plate 2' has been developed so as to be used in the thin type friction pad 1', the length L.sub.1 ' being expressed by the following equation: EQU L.sub.1 '=L.sub.2 '+S'+a=L.sub.1 -.DELTA.S (2)
However, the above-described friction pads 1 and 1' having the corresponding backing plate thickness S and S' must be provided with the correct corresponding wear limit warning pieces 6 and 6'. Therefore, there is a danger of erroneous provision of the wear limit warning piece 6 and the backing plate 2' or the wear limit warning piece 6' and the backing plate 2 in the manufacturing process. In order to prevent erroneous assembly of the parts described above, it is necessary to provide, for example, an identification mark or the like on each of the friction pads 1 and 1' and the wear limit warning pieces 6 and 6'. However, this results in an unwelcome increase in the number of administrative and assembly processes.